Ultra stable optical element x,y, positioning unit for use in harsh environments

ABSTRACT

An X, Y positioning unit, mount or fixture is designed to adjust the position of an optical element mounted in the fixture so as to move it laterally and vertically with respect to the optical axis of the element, such that, once adjusted, the position is maintained through the clamping of plates about the positioning fixture to lock the hinges against movement. In this manner the adjusted position of the optical element is locked with high forces exerted by the plates on the fixture, with the locking technique not affecting the alignment. In one embodiment, the fixture includes live hinges which join an optical element holder to a fixed plate and pivot the holder about orthogonal axes crossing at the center of an optical element holder such that small movements of the hinged holder about the hinges adjusts the position of the center of the optical element holder and thus the optical element. The fixture in a preferred embodiment includes a milled block of metal having slots Electric Discharged Machined or High Speed Machined therein to leave thin flexible hinges, with positioning screws utilized to move the optical element holder about the hinges. When the appropriate adjustment has been made, the holder is clamped in the adjusted position to the fixed plate through the use of the clamping plates to provide a rigid structure capable of withstanding high static and dynamic loading. For laser target designator applications, positioning unit tolerance is less than one half micron, resulting in target designation boresight alignment errors less than 500 microradians.

FIELD OF INVENTION

This invention relates to optical alignment equipment and moreparticularly to a method and apparatus for precisely aligning opticalelements and maintaining the alignment in the presence of harshenvironments.

BACKGROUND OF THE INVENTION

It will be appreciated that optical alignment systems have includedflexible hinge type mechanisms for positioning the optical axis of anoptical element through flexure of live hinges. By live hinges, what ismeant is a necked-down area on a solid object, being made thin enoughthat it forms a flexure, allowing one solid portion of the object tomove with respect to the solid portion on the opposite side of thenecked down region. This movement is pure rotation about the hinge, butfor a small angle approximates linear motion. Usually, the elastic limitof the material from which the object is made will allow a few degreesof motion before plastic deformation occurs. Sometimes plasticdeformation of the live hinge is allowed, and causes no problem, as longas repeated adjustments are not to be made. The typical deployments ofthese types of hinges are not particularly well suited for harshenvironments because they are usually designed for use in a laboratory,in which the conditions are carefully controlled as to temperature,humidity and mechanical stress. Usually these elements are made up ofmultiple materials of different thermal coefficients of expansion andgenerally do not have lock down mechanisms. If they do, the lock downmechanisms deleteriously affect the previously made adjustments.Moreover, laboratory alignment fixtures are not sufficiently robust whenused outside the laboratory such as for laser target designators,communications systems involving lasers or in surveying equipment.Additionally, unless ruggedized and specially designed, laboratoryfixturing apparatus for the alignment of optical elements isunacceptable for military and commercial applications because opticalalignment is severely affected by changing environmental conditions.

For instance, if a laser target designator is mounted on an aircraft,when the aircraft is in the vicinity of a target, the designator isutilized to mark the target by illuminating the target with laserradiation. The way this is usually accomplished is to first obtain avisual image of the target, with the target centered in the crosshairsof a screen. It is then incumbent upon the target acquisition system tobe able to position a laser beam exactly along the optical axis thatresulted in the visual image. In this manner the visual image isco-boresighted with the laser axis, or visa versa.

In tactical situations, target acquisition requires accuracy ofapproximately plus or minus three feet in order to be able to accuratelydirect an ordinance to a particular target. If the laser designated spotis displaced by a significant amount, for instance 20 feet, then theordinance may miss its target altogether. Thus it is possible thateither a tank will not be properly illuminated or that a missile silocan be missed.

In one operating scenario, the aircraft stands off from the target, forinstance, one mile and illuminates the appropriate target by providingthat the crosshairs on the visual image corresponds to the portion ofthe target to be illuminated. The plane then executes a high G roll andflies away from the target with the laser target designating equipmenttracking the target as the aircraft executes its maneuvers.

It will be appreciated that aside from the system dynamics of the lasertarget designator, the precision by which the laser is co-boresightedwith the optical image depends in large part upon how accurately thesystem was aligned to begin with. This means, for instance, when usingone laser beam to end-pump a small crystal of another laser, such as adesignator laser, the pump beam must be accurately focused into thelasing material. If the pump laser is mounted remotely from thedesignator laser compartment, the output of the pump laser can betransmitted through a fiber optic link and focused on the pump region,typically in a 0.1 millimeter or less wide volume within the laser rod.

This focusing operation is highly critical, with any off centering ofthe pumped radiation in the laser rod causing a loss of laser power andboresight alignment.

The pump laser is mounted remotely because one does not want tointroduce excess waste heat in the region of the designator laser cavityor compartment. The heat generated by the pumping laser is sometimesreferred to as self-contamination, which can cause a shift of theoptical elements resulting in boresight error.

Typically in such an environment, it is important to be able toaccurately position the distal end of the optical fiber relative to acollector lens and a focusing lens assembly so that light from thedistal end of the fiber is appropriately focused in the aforementionedpump region of the laser rod. So precise is the positioning requirementfor the end of the fiber optic cable that lateral movement of the cableof greater than one half-micron results in reduced laser power, andpossibly boresight error, due to movement of the focused radiation, andthus the pump region within the laser rod. For a two-millimeter laserrod, the pump region is typically on the order of 0.1 millimeter indiameter.

Even with the optical fiber termination being appropriately positionedduring an alignment procedure, if due to the aforementioned harshenvironment lateral positioning errors build up and exceed the onehalf-micron limit, then the laser beam which creates the laserdesignator spot can be off by as much as 20 feet at a standoff distanceof one mile.

As mentioned, a laser beam displaced by 20 feet can result in acompletely missed target or the illumination, sometimes referred to aspainting, of an unintended target.

From the point of view of laser target designators, the pointingaccuracy of the entire system typically must be less than 0.5milliradians. While there are indeed many factors in the laser targetdesignation system which can contribute to boresight error, it isincumbent upon the laser itself to contribute as little as possible tothis error. The laser, as a component of a designator system may only beallowed as much as 0.2 milliradians of boresight error, and a 10% energydrop over the entire environmental range of changing temperatures,pressures, accelerations, self contamination loading, and acoustics.

Another application that requires the ultimate in boresight accuracy isin the area of countermeasures. In these types of environments anincoming missile is to be countered. This requires firing a modulatedlaser beam towards the incoming missile with such accuracy that the beamimpinges on the missile as it approaches its target. Sometimes the timewindow for acquisition and beam deployment is less than two seconds.Moreover there must be enough laser power illuminating the missile tocounter it. This requires highly accurate aiming, which cannot bedeleteriously affected by misalignments of the optical elements on theoptical bench. Such countermeasures require the same alignmentaccuracies as discussed above, the 0.5 milliradian accuracy.

There are however other applications for an X, Y positioning fixture orunit for optical elements, not the least of which is when one is tryingto couple the ends of opposed single mode fibers. A single mode fiber,such as might be used in a fiber optic telecommunications system, iscommonly less than ten microns in diameter. Assuming that the two fibersare to be aligned along the same optical axis, one would commonlyrequire having a one half-micron transverse alignment accuracy andstability in order to successfully couple one fiber to the other withless than 0.4 dB splice loss. Certainly, there are other applicationswhere the alignment requirements are even tighter, and where theprecision alignment must be maintained in harsh environments involvinglarge temperature swings as well as high dynamic and static loadingconditions.

Moreover, for optical communications it is important that the lasersource illuminate the intended receiver. When, for instance, providinglaser communications between an over flying satellite and an earthstation, any positioning errors will affect the receipt of informationcontained on the beam. Free space laser communications devices arebecoming more important in commercial and military applications. To keepcommunications secure, narrow beam divergences and accurate pointingwill be necessary qualities of these systems. In this scenario, as wellas those presented above, boresight alignment is critical. In order toachieve the necessary stringent tolerances, the optical elementsthemselves must be accurately aligned and must maintain their alignment.There is therefore a need for a robust device for achieving alignmentand preserving it in harsh environments.

SUMMARY OF THE INVENTION

In order to maintain the original alignment of optical elements, in thesubject invention a positioning unit, mount or fixture is utilized inwhich X, Y centering of the optical element is achieved through theutilization of a unit having two live hinges for controlling themovement of the optical element in two orthogonal directions. The hingesthemselves are located along the X and Y axes respectively and involvethe utilization of a block of material having slots machined orotherwise provided therein to form thin flexible hinge elements.Setscrew activation or other means of positioning the optical elementresults in movement of an optical element holder about these two hingessuch that in one embodiment adjustment of the optical element isachieved with a one half-micron accuracy. Having adjusted the lateralposition of the optical element appropriately, it is then incumbent uponthe system to provide for a locking mechanism, which does not affect theoriginally aligned elements.

While in the past, locking screws and other devices have been utilized;the locking screws themselves when tightened down affected the originalalignment.

In the subject invention once the optical element holder has beenappropriately aligned, clamping plates to either side of the blockcontaining the hinges are clamped together such that by clamping theplates together the original optical alignment is maintained.

The structure thus formed in essence is a single unitary structure withthe positions of the individual parts maintained through friction formedby the high clamping pressure of the plates. The clamping is arranged sothat there is no loading of the parts in directions that affect thealignment prior to clamping. Moreover, the material of which theclamping plates are made matches the thermal coefficient of expansion ofthe block so that changes in temperature affect all parts of thestructure identically. The structure with the locking plates being madeof the same material react identically to temperature changes, withstructural rigidity of the structure resisting alignment changes in theface of dynamic and static loading. Furthermore, the relatively largearea and high pressure achieved in the clamping action acts to reducethe thermal resistance from the clamping plates to the block,effectively reducing the occurrence of temperature gradients across theunit and enhancing stability.

The only elements that are not typically made from of the same materialas the adjustable element are the locking screws, which because of theirplacement orthogonal to the direction of adjustment have little to noeffect on the lateral adjustments themselves. This is because there isno resultant load in these two orthogonal directions. The lockingscrews, once tightened, are in a highly preloaded condition; and thechange in clamping pressure experienced due a temperature change of theblock and clamping plates of one material and the locking screws ofanother is absorbed across the area of the clamping plates, a relativelylarge area when compared to the locking screw head and washer.

High stress may be developed in the tiny hinge region during adjustmentnear the extreme ends of the adjustment range, which is usually not morethan a few degrees. This high stress is not a detriment to thefunctioning of the unit, because the locking sandwich around theadjustable block forms a clamped, laminate structure that is verystrong. Even in the case where the stress is locked in by the clamps,causing creep to occur in the hinge over time, the clamping plates sotightly grip the adjustable element that the force induced there can beignored. This is true in part, because the tiny hinge region, where thestress is high, is very small with respect to the adjustable element.This relatively small aspect ratio of hinge area to clamped area keepsthe high stress from causing high force or what would be perceived ashigh force by such a large clamp. Instead, the high stress is able tomanifest itself as harmless creep in the hinge, until the clamp isreleased at some future time, if it is ever released at all. In otherwords, if the creep strength of the material is exceeded duringadjustment the unit might exhibit a shift in adjusted position at somefuture date when un-clamped. This will not affect the accuracy,resolution or stability of the unit if the clamping plates are deployedand left in place.

In summary, an X, Y positioning unit, mount or fixture is designed toadjust the position of an optical element mounted in the fixture so asto move it laterally and vertically with respect to the optical axis ofthe element, such that, once adjusted, the position is maintainedthrough the clamping of plates about the positioning fixture to lock thehinges against movement. In this manner the adjusted position of theoptical element is locked in by high forces exerted by the plates on thefixture, with the locking technique not affecting the alignment. In oneembodiment, the fixture includes live hinges which join an opticalelement holder to a fixed plate and pivot the holder about orthogonalaxes crossing at the center of an optical element holder such that smallmovements of the hinged holder about the hinges adjusts the position ofthe center of the optical element holder and thus the optical element.The fixture in a preferred embodiment includes a milled block of metalhaving slots made by Electric-Discharge-Machining (EDM) or High SpeedMachining (HSM), or by stacking several thin layers made by etchingtherein to leave thin flexible hinges, with positioning screws utilizedto move the optical element holder about the hinges. When theappropriate adjustment has been made, the holder is clamped in theadjusted position to the fixed plate through the use of the clampingplates to provide a rigid structure capable of withstanding high staticand dynamic loading. For laser target designator applications,positioning unit tolerance is less than one half micron, resulting intarget designation boresight alignment errors less than 0.5microradians.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the subject invention will be betterunderstood in connection with the Detailed Description in conjunctionwith the Drawings, of which:

FIG. 1 is a diagrammatic illustration of the operation of a laser targetdesignator illustrating the requirement of precision boresight accuracyto prevent misidentification of targets through a displaced laser beam;

FIG. 2 is a diagrammatic illustration of the laser target designatorscenario of FIG. 1, illustrating the reversal of direction of theaircraft utilized in the target illumination after having designated aparticular target by placing the crosshairs of the visual image on theintended illumination point;

FIG. 3 is a diagrammatic illustration of a pumped laser for use in atarget designation system illustrating the relatively small pump regionfor the laser in which a pumping diode is connected via fiber opticsthrough the subject X, Y positioning unit so as to appropriately focusthe pumped energy in the pump region;

FIG. 4 is a diagrammatic and side view of the subject live hinge X, Ypositioning unit illustrating a downward deflection of the hinged memberthrough flexure of the hinge, thus to drive the center of the fiber orfiber bundle end in a controllable downward direction;

FIG. 5 is a diagrammatic illustration of the movement of the fiber orbundle end of FIG. 4 illustrating a Y axis downward correction throughflexure of the live hinge of FIG. 4;

FIG. 6 is a diagrammatic illustration of the subject X, Y positioningunit illustrating the addition of a live hinge to permit adjustment ofthe center of the fiber/bundle end through the flexure of thisadditional live hinge so as to create motion in a lateral or transversedirection;

FIG. 7 is a diagrammatic illustration of the displacing of the center ofthe fiber/bundle end in the X direction;

FIG. 8 is an exploded view of the subject X, Y positioning unitillustrating the utilization of clamping plates to either side of thebody of the unit so as to sandwich the body therebetween, with theclamping of plates locking in the adjustments previously made;

FIG. 9 is a cross sectional view of the subject X, Y positioning unitillustrating orthogonally positioned live hinges to permit vertical andlateral adjustment of the optical element holder, illustrating thealignment of the live hinges respectively on a horizontal axis on thecenter of the optical element holder and the vertical axis passingthrough the center of the optical element holder; and,

FIG. 10 is a diagrammatic illustration of the utilization of the subjectX, Y positioning unit to position opposing ends of a single mode fiber,illustrating the need for one half micron positioning accuracy.

DETAILED DESCRIPTION

Referring now to FIG. 1, in a tactical situation an airborne lasertarget designator 10 is carried by an aircraft 12 which is utilized toilluminate a target 14 which may be a particular window in a building 16surrounded, for instance, by a stack 18 and an outlying building 21.

During the laser target designator process, the aircraft, which may bestanding off by as much as one mile, acquires the visual image of thetarget on a screen 22 having a crosshair in the center thereof. Theentire optical system is maneuvered around so as to visually center theilluminated target, namely window 14 on crosshairs 24. When thecrosshairs designates the intended target, a target lock system 30 isengaged to have the laser target designator lock onto the target, inthis case window 14, at which point a laser beam is projected towardsthe target.

The laser target designator includes a visual image system 32, which hasas its boresight dotted line 34. It will be appreciated that opticalaxis 34 of the visual image presentation system is centered on target14.

It is the purpose of the laser target designator to provide that theoutput of a laser 36 having a boresight axis 38 be collinear with ormatched to the visual image optical axis 34.

The degree of accuracy of the alignment of the laser beam with thevisual image boresight is quite critical. From an operational point ofview, the illuminated spot on the target must be within approximatelythree feet of the actual target. The precision by which the intendedtarget is illuminated depends of course upon the aiming optics of thelaser.

However, before considering the accuracy of the aiming optics of thelaser, it is important that the laser boresight be accuratelyestablished.

This is ordinarily done by an alignment procedure in which a remotelymounted pump laser has its energy focused at a predetermined pump regionwithin a laser rod. If the pumping radiation is not appropriatelyfocused, for instance, to within a 0.1 millimeter region within thelaser rod, then it is possible that even if there are zero pointingerrors in the pointing system, a displaced laser beam 40 may result inwhich at a 5,000 foot standoff distance may be displaced by as much as20 feet.

This inaccuracy can result, for instance, in the targeting of anunintended target such as an outbuilding or a smoke stack, as opposed tothe intended window in the FIG. 1 scenario.

As illustrated in FIG. 2, once the laser target designator has initiallylocked onto the target, the aircraft typically executes an evasionmaneuver which in general causes the aircraft to veer away from thetarget while having the laser target designator 10 illuminate thetarget. This evasive maneuver causes extreme dynamic loading on allaspects of the optical bench utilized in the laser target designatorwhich if not mechanically robust can result in the aforementioneddisplaced laser beam.

Not only is the optical bench of the laser target designator subjectedto both static and dynamic loading, temperature variations can causeoptical element misalignment. It is therefore important to be able toprovide an adjustable mounting system for optical elements which cansurvive vibration, and static and dynamic loading to preserve theoriginal alignment of the optical elements. It is also important thatwhatever is utilized to lock down the alignment not have a thermalco-efficient of expansion different from that associated with themounting apparatus itself.

One of the problems limiting the use of alignment mounts has been thedifficulty in locking the alignment once it has been set. If setscrewsare utilized to set the alignment, once the correct alignment has beenobtained these screws are tightened to prevent any additional movementof the fixture when the system is exposed to shock and vibrationenvironments. However, this tightening procedure is may result inaltering of the original alignment if the tightening changes thealignment. Prior system have tried to balance the affect of tighteningthe screws but the alignment process utilizing such a tighteningprocedure is time consuming and difficult.

Moreover, using a lock nut and tensioning it also can affect theoriginal desired alignment making the lock nut adjustment screwcombination undesirable.

The criticality of the optical alignment in one embodiment isillustrating in FIG. 3 to show how critical the alignment of thetermination of a fiber optic cable is when a pumping diode is utilizedto provide energy to a rather small pump region within the laser rod.

In FIG. 3, it will be seen that a laser rod 50 has a pump region 52which can be as small 0.1 millimeter on a side. It is important that theoutput of a pump diode 51 transmitted through fiber optics 54 and aterminus 56 be focused precisely on pump region 52. In order for thefocusing to be exact, an X, Y positioning unit 60 is utilized toposition the end 62 of the fiber optic cable precisely in two orthogonaldirections.

The light from end 62 is focused by a collector lens assembly 64 whichtransmits collimated light to a focus lens 66 which when reflected by amirror 68 through an end 70 of the laser cavity housing the laser rodfocuses the radiation from end 62 of fiber optics 54 into the pumpregion. Here it will be seen that at the other end of the laser cavityis the partial reflector optic 72 which forms the output of the laser ata wavelength λ2 and thus the laser target designator. It will beappreciated that the wavelength of the pumping diode is different fromλ2.

Should the output of the pumping diode not be appropriately accuratelypositioned in pump region 52, then there are two untoward events. First,the laser power is significantly reduced. However, more importantly,laser boresight alignment is degraded. The degradation of the boresightalignment is significant and can by itself result in a displacement ofthe target illuminator's spot by as much as the aforementioned 20 feetin the above example. It can be shown that the positional accuracy ofthe X, Y positioning unit must be less than one half micron in orderthat the angular boresight error of the laser target designator be lessthan 0.5 milliradians.

Not only must the alignment be perfect with respect of illumination ofthe pump region by the pumping laser, all optical elements on theoptical bench for the laser target designator must be positioned to thisaccuracy.

While the subject invention will be described in connection withaccurately positioning the terminus of a fiber optic cable, its use forpositioning of any optical element is within the scope of the subjectinvention. Thus, for instance, optical elements such as lenses, prisms,corner reflectors, and the like may be accurately and robustlypositioned through the subject X, Y positioning unit.

As will be seen through the utilization of two live hinges and aclamping sandwiching locking mechanism, the original alignment affordedthrough the live hinges can be preserved against high dynamic and staticloading so as to preserve the one half micron alignment accuracy.

Referring to FIG. 4, the live hinge positioning fixture or mount of thesubject invention is illustrated. Here positioning unit 60 isillustrated as having a mechanically fixed portion 70 connected to anadjustable movable portion 72 through flexure of a live hinge 74. Thecenter of flexure 76 of hinge 74 is located along a horizontal axis 78which passes through the center 80 of an optical element receivingaperture 82 in the associated holder 83.

Adjustment of the position of center 80 is accomplished through movementof portion 72 in one embodiment through the turning of a setscrew 84such that portion 72 moves downwardly as illustrated by arrow 86 so asto come to a position illustrating by dotted line 88. It will beappreciated that center 80 moves along an arc 90 in accordance with theflexure of hinge 74. Note that portion 72 moves as indicated by doubleended arrow 92.

Referring to FIG. 5, it can be seen that aperture 82 moves downwardly inthe Y direction as illustrated by dotted line 82′ upon flexure of pivot74 due to the action of setscrew 84. This describes the verticaltranslation of center point 80.

With respect to horizontal translation of center point 80 and referringnow to FIG. 6, a second live hinge 100 is positioned along axis 102which passes through center point 80 and is orthogonal to axis 78.Portion 72 is moved laterally by setscrew 104 such that portion 72pivots about pivot point 100 as illustrated by double arrow 106 so as togo along path 108.

Referring to FIG. 7, upon adjustment as illustrated in FIG. 6, aperture82 is translated horizontally along the X-axis as illustrated by 82″.

Having the two live hinges as illustrated in FIGS. 4 and 6, orthogonaltranslations of the aperture containing the optical element are easilyachieved through an easy quick adjustment procedure.

Once having achieved the initial adjustment, it is important to be ableto secure portions 72 and 70 so that they do not move relative to eachother. What this means is that there can be no more flexure about livehinges 74 and 100 once the initial adjustment has been made.

How this is accomplished is illustrated in FIG. 8 in which the portions70 and 72 are clamped in place through the sandwiching action of plates120 and 122 through the use of a bolt 124 which passes through a washer126 and an oversized aperture 128 in plate 120. The bolt then passesthrough another oversized aperture 130 in portion 72 of unit 60 and thento a threaded aperture 132 in plate 122.

Each of the sandwiching plates is secured at one edge through bolts 134so that they are maintained in place and in one embodiment spaced fromsurface 136 of portion 72 so as to permit free motion of this portionduring the adjustment process.

Once the adjustment has been made, the plates are flexed inwardly asillustrated by arrows 123 and 125 through turning bolt 124. The movementof plates 120 and 122 in a clamping position does not load portions 70and 72 in a manner that would alter in any way the originally setposition. This is because the force applied is normal to that whichwould be associated with flexure of either of the live hinges, thedirections of adjustment.

The result is an extremely mechanically stable mounting system foroptical elements which can be easily initially adjusted through theutilization of live hinges and setscrews and which position, oncealigned, can be locked in through the utilization of clamping plates toeither side of the device. This clamping exerts a high force that holdsthe adjustable element and the live hinges in place, without cross talkin the direction of adjustment.

In short, once the alignment is set, the sandwiched clamping arrangementclamps in the adjusted positions without affecting the process.

Referring to FIG. 9, in one embodiment where like reference charactersbetween FIGS. 8 and 9 indicate like elements, aperture 80 may beutilized to clamp any optical element including a lens for thepositioning thereof in the X and Y directions. Here a slot 140 is formedin portion 72 to permit the clamping of the optical element in aperture80 through the use of a bolt 142 which clamps the optical element inplace. This optical element can be the terminus of a fiber optic cable,a lens, corner cube or in fact any element, the lateral position ofwhich is to be controlled. Here live hinges are illustrated at 74 and100. It can be seen that setscrew 84 produces the same downward motionof portion 72 as that illustrated in FIG. 4. However, setscrew 84 inFIG. 9 enters from the right through an easily accessible aperture 146.Moreover, setscrew 104 controls flexure around pivot 100 and isaccessible from the right through aperture 148. This means that the twosetscrews used in adjusting portion 72 are accessible from one side ofthe fixture or mount, thus providing easy accessibility.

It will be appreciated that not only can optical elements beappropriately positioned by the subject X, Y positioning fixture orunit, as illustrated in FIG. 10 the ends 150 and 152 of opposed singlemode fibers 154 and 156 may be adjusted so that they have a commonoptical axis 158. The adjustment of abutting single mode fibers isindeed critical since the diameters of the fibers themselves may be onlyeight microns, or less. What this means is that the position of ends 150and 152 must be accurate to one half micron in order to sufficientlysustain the coupling between the single mode fibers.

Through the utilization of the subject X, Y positioning unit 60 at theend of each of these fibers is possible to achieve the butt-to-buttalignment of the single mode fibers, thus to support the single modeoperation. Moreover, the alignment will be maintained, even in a harshenvironment, including cryogenic environments, or energetic, dynamicenvironments.

Having now described a few embodiments of the invention, and somemodifications and variations thereto, it should be apparent to thoseskilled in the art that the foregoing is merely illustrative and notlimiting, having been presented by the way of example only. Numerousmodifications and other embodiments are within the scope of one ofordinary skill in the art and are contemplated as falling within thescope of the invention as limited only by the appended claims andequivalents thereto.

1. Apparatus for the positioning of an optical element, comprising: abase having a slot therein for defining a live hinge, thus to divide thebase into a fixed portion and a moveable portion joined by said hinge,said moveable portion including an optical element holder having acenter; an adjustment unit for moving said moveable portion to anadjusted position, thus to flex said hinge; clamping plates ondiametrically opposite sides of said base so as to sandwich said basetherebetween, said plates when clamped together adapted to engage saidopposite sides to prevent flexure of said live hinge; and, means forclamping said plates together after achieving said adjusted position,thus to lock in said adjusted position, whereby clamping said platespreserves said adjusted position without altering said adjusted positionduring the locking procedure.
 2. The apparatus of claim 1, wherein saidlive hinge lies on an axis through the center of said optical elementholder.
 3. The apparatus of claim 2, wherein said optical element has anoptical axis and wherein said live hinge axis is orthogonal to saidoptical axis.
 4. The apparatus of claim 1, wherein said moveable portionhas a slot therein defining a second live hinge for permitting motion ofsaid moving portion in a direction orthogonal to that associated withsaid first-mentioned hinge, thus to permit adjustment of the position ofsaid optical element holder in orthogonal directions and furtherincluding a second adjustment unit for moving said moveable portion in adirection orthogonal to the direction associated with flexure of saidfirst-mentioned hinge, thus to provide adjustment of the position ofsaid optical element holder in two orthogonal directions.
 5. Theapparatus of claim 4, wherein said second live hinge is centered on aline running through the center of said holder and orthogonal to a lineabout which said first-mentioned hinge flexes, said last mentioned linerunning through the center of said holder.
 6. The apparatus of claim 1,wherein said adjustment unit includes a screw having a tip contacting asurface of said block.
 7. The apparatus of claim 4, wherein saidadjustment units are accessible from one side of said block.
 8. Theapparatus of claim 7, wherein said adjustment units are located in saidfixed portion of said base.
 9. The apparatus of claim 1, wherein saidplates are initially spaced from said diametrically opposite side topermit adjustment of said moveable position of said base prior toclamping, thus to facilitate unfettered adjustment of the position ofsaid optical element holder.
 10. A method for preserving alignment of anoptical element in an adjustable position holder secured to a basehaving opposed sides comprising: clamping plates to diametricallyopposite sides of said base so as to maintain said holder in theposition established before clamping, thus to eliminate the necessity ofproviding locking apparatus which affects the originally establishedholder position.
 11. The method of claim 10, wherein the position of theholder is established through the use of at least one live hinge, theclamping plates freezing the position of the hinge.
 12. A method ofaligning opposed single mode optical filters, comprising the steps of:locating each of the ends of the filters in an X, Y positioning fixtureadjustable to sub-micron accuracy; and, adjusting the position of theends of the fibers to lie along a common optical axis using the X, Ypositioning fixture.
 13. The method of claim 12, wherein each X, Ypositioning fixture includes a block with at least one live hinge thatprovides adjustability of a movable portion of the block in X, Yorthogonal directions, the movable portion including a holder for theend of an optical fiber, and further including the step of locking thehinge in place after adjustment.
 14. The method of claim 13, wherein thelocking step includes clamping plates to either side of the fixture toprevent movement of the live hinge.